condition001
Plastic
- Joined
- May 18, 2020
- Location
- Idaho, USA
Hi all,
I have a fairly unique starting problem with a rotary phase converter I'm helping a friend build. The motor we're using is a 10HP 1760 RPM off of an old air compressor. It works great on 3-phase power and even starts quite well as a Fitch Williams rotary phase converter...MOST of the time.
The problem we're running into is that there seem to be three positions the shaft can be in (~120 degrees apart) where the starting circuit, even with 675uF of starting capacitors all in, fails to spin the motor up but leaves the motor growling and frozen in place. If the converter is started with the shaft in ANY other position (we're talking less than 5 degrees rotation here), it spins up so quickly that it jumps a little on the cart.
To test the capacitors and starting circuit, we hooked up two other motors (7.5HP and 15HP), one at a time, and both started quickly every time (which seems to indicate that the capacitors are good and also of a sufficient quantity for the 10HP). We've confirmed that the 10HP motor is wired correctly for 240v (and not 480v) and that all connections are tight.
This problem has been constant from 400uF worth of start capacitors all the way up to the 675uF currently in place. Changes were made in about 50uF increments.
Testing is being done with a 50A circuit supplying power an appropriately sized magnetic contactor switching the motor power on/off and another appropriately sized contactor switching the start capacitors in/out of the circuit.
We're using the Fitch Williams diagram (found here: https://www.practicalmachinist.com/FitchWConverter.pdf) and are trying to get the basic operation going. No run capacitors or power factor capacitors have been added yet.
Does anyone have any thoughts on this? We're stumped, especially where the only variable causing issues seems to be the motor itself, but only in those three small ranges. Any help would be greatly appreciated!
I have a fairly unique starting problem with a rotary phase converter I'm helping a friend build. The motor we're using is a 10HP 1760 RPM off of an old air compressor. It works great on 3-phase power and even starts quite well as a Fitch Williams rotary phase converter...MOST of the time.
The problem we're running into is that there seem to be three positions the shaft can be in (~120 degrees apart) where the starting circuit, even with 675uF of starting capacitors all in, fails to spin the motor up but leaves the motor growling and frozen in place. If the converter is started with the shaft in ANY other position (we're talking less than 5 degrees rotation here), it spins up so quickly that it jumps a little on the cart.
To test the capacitors and starting circuit, we hooked up two other motors (7.5HP and 15HP), one at a time, and both started quickly every time (which seems to indicate that the capacitors are good and also of a sufficient quantity for the 10HP). We've confirmed that the 10HP motor is wired correctly for 240v (and not 480v) and that all connections are tight.
This problem has been constant from 400uF worth of start capacitors all the way up to the 675uF currently in place. Changes were made in about 50uF increments.
Testing is being done with a 50A circuit supplying power an appropriately sized magnetic contactor switching the motor power on/off and another appropriately sized contactor switching the start capacitors in/out of the circuit.
We're using the Fitch Williams diagram (found here: https://www.practicalmachinist.com/FitchWConverter.pdf) and are trying to get the basic operation going. No run capacitors or power factor capacitors have been added yet.
Does anyone have any thoughts on this? We're stumped, especially where the only variable causing issues seems to be the motor itself, but only in those three small ranges. Any help would be greatly appreciated!